Automatic ringing and secret-service telephone system.



H-. D. CURRIER.

AUTOMATIC RINGING AND SECRET SERVICE TELEPHONE SYSTEM.

I APPLICATION- FILED APR. 10, [913. v lfl-y2839196n I Patnted July 10, 1917.

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H. D. CURRIER. 4

AUTOMATIC RINGING AND SECRET-SERVICE TELEPHONESYSTEM. APPLICATION FILED APR. 10, 1913.

1,238,196 Patented Ju1y10,1917.

4 SHEETS-SHEET 2.

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AUTOMATIC RINGING AND SECRET SERVICE TELEPHONE SYSTEM.

APPLICATION FILED APR. 10, 1913.

4 SHEETSSHEET 3.

1 288 196 Patented July 10, 1917.

H. u. CURRIER.

AUTOMATIC RINGING A ND SECRET SERVICE TELEPHONE SYSTEM.

APPLICATION FILED APR. 10, 1913.

LQW, T 96., Patented July 10, 1917.

4 SHEETS-SHEET 4.

. 1 N Z/ 21272755555? v .ZZYUEfZZEF: g Efamflflurrz'er M wg w HZZbPnQy tartan sra'rns rarnnr orrion HIRAIVI D. CURRIER, OF CHICAGO, ILLINOIS, ASSIGNOR TO KELLOGG SWITCHBOARD AND SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

AUTOMATIC RING-ING AND SECRET-SERVICE TELEPHONE SYSTEM.

mamas.

Specification of Letters Patent.

Patented July 10, 1917.

Application filed April 10, 1913. Serial No. 760,119.

To all whom it may concern:

Be it known that I, I-IIRAM D. CURRIER, a citizen of the United States of America, residing in Chicago, county of Cook, and State of Illinois, have invented certain new and useful Improvements in Automatic Ringing and Secret-Service Telephone Systems, of which the following is a specification. 4

My invention relates to link circuits for telephone systems, being directed more par ticularly to link circuits having automatic ringing andsecret service. By secret service I mean a circuit in which the operators telephone cannot be operatively associated with the link circuit while the link circuit is connecting a calling and a called substation in a conversational circuit. By automatic ringing systems I mean those systems in which after the ringing current has been applied to the called line, it is automatically disconnected when the subscriber at the called substation responds. One of the objects of my invention is to provide a link circuit of the above character in which four relays only are used for controlling the supervisory and secret service system and also the ringing system. Other objects of my invention will be hereinafter more particularly pointed out.

I have preferably embodied my invention in an operators cord circuit and in carrying out my invention when applied to the so-called four relay arrangement I employ an answering supervisory relay which is energized when the answering end of the link circuit is connected to a calling line whereby the operators telephone is connected in circuit with the calling substation. A second relay is also provided in the nature of an operators disconnect relay which operates when the calling end of the link circuit is connected to the called line, such operation of the relay effecting the discon-' nection of the operators telephone. A third relay in the nature of a ringing control relay is provided which is adapted to be operated upon a response from the called substation to disconnect the ringing current from the called line and a fourth relay in the nature of acalling supervisory relay is also provided by which a called-station vention in which no listening key is required and in which it is impossible to associate the operators telephone with the cord circuit while it has its answering and call ing ends connected to telephone lines;

Fig. 2 illustrates a cord circuit having the same method of operation as Fig. l but applied to a three conductor cord and line circuit Fig. 3 illustrates a three conductor cord circuit in whichthe operators telephone is connected in operative relation with the cord circuit when the call is answered and disconnected upon being connected to a called line and then by the use of an operators key may be again associated with the link circuit only if one or both receivers are on their switch-hooks;

Fig. 4t is a three conductor operators cord circuit having the features of Fig. 4 but in which it is necessary for the operator to throw a key each time the operators telephone is to be associated with the cord circuit;

Fig. 5 illustrates the manner of combining a relay and impedance coil so as to mount them on a single axis,

Fig. 6 illustrates the preferred adjustment of the ringing control relay; and

Fig. 7 illustrates diagrammatically the balanced cord circuit of Fig. 1.

Referring now to Fig. 1, I have illus trated two lines A and B of a well known socalled two-wire multiple type having wellknown forms of substations C, D respectively and line circuits E, F, at the central ofiice. Each of the line circuits includes a line relay LR and a cut-ofl relay CO together with multiply connected jacks J. The calling circuit E has its parts indicated by the large reference characters and the called line circuit F has its parts indicated by small reference characters.

The operators cord circuit G is adapted for interconnecting the telephone lines and has'an answering plug P and a calling plug 72 connected by so-called tip and sleeve conductors having the condensers 1 and 2 interposed. A relay AS is associated with the answering end of the cord circuit thisrelay signal 3 is controlled by relay lay AS which is controlled over the calling servingas an answering supervisory relay and also for associating an operators telephone set O with the link circuit when a call is answered. An answering supervisory line is connected to one terminal of a centrialzoflice telephone battery, the other ter minal of battery being connected through an impedancecoil I to the other strand of the link circuit so a'sjto bridge the central ofiice battery across the talking conductors for talking and supervisory purposes.

A third relay OD is connected to the calling endof the link circuit, being in the nature of an operators disconnect relay in that it disconnects the operators telephone from the link circuit when the calling plug 7) is connected to the called line. Due to the -fact that in the present embodiment of my grelay OD upon connecting to a called line invention the operators' telephone is connected through normally closed contacts of relay OD, it will be apparent that as long as plug P is in connection with the terminals of a line circuit, the operators telephone 0 is associated from, the link circuit giving a so-called secret service in which the operator cannot listen in during a connection between two telephone lines. The operation of also' is eifective to connect ringing current vvound upon the core of ROB,

from one of the ringing generators of ringing apparatus H to the termlnals of the called line and when a response 18 secured from the substation on this line the ringing united so that the ringing current will not flow back over the calling line and I have preferably provided contacts upon the relay ROR which are adapted to control the continuity of the talking conductors and to disconnect the ringing current. Furthermore,

meansmust be provided whereby when the ringing current is disconnected upon re sponse of the called subscriber such ringing current will not be'again applied when the subscriber replaces his receiver upon its switch-hookand to this. end a locking contact 6 and locking winding 7 are provided for control relay ROB so that when it-once energizes it will remain energized until the AS. The recalling plug 72 is withdrawn from the jack. This places considerable work upon the relay BUR, for a relay which must energize over the called line, and therefore I have provided an improved adjustment and control of relay FOR whereby the initial energizing circuit for this relay (which is over the called line) attracts its armature under the tension of a single spring 6 only until. the alternate contact 6 is closed and the local energizing and locking circuit 7 included, at which time the continued attraction of the armature operates the other springs 8, 9, upon this relayas shown in Fig. (5. An advantage of such arrangement is that this relay ROB which is initially energized over the called line circuit starts the attraction of its armature under the tension of but a single contact spring until this local circuit is closed after which the other springs are operated and in this way a comparatively large number of contacts may be operated by a relaywhich is initially controlled over a circuit, which may vary considerably in resistance.

A supervisory signal 10 is associated with the calling plug 7) and this signal becomes lighted when the plug 7) is inserted into a jack j of the called line, which is the usual period, and when the called subscriber responds this lamp 10 must be efiaced. To this end I have provided the calling supervisory relay OS which is adapted to be energized by current over the called line so that the subscriber at the called substation has control of this relay OS and therefore of lamp 10. Thus, when the called subscriber has responded, talking current is supplied to the called line from the central battery through the relays CS and OD.

' To the end that the relays and impedance coil I of cord circuit G may be mounted in the least possible space, I combine the impedance coil I and one of the supervisory relays as is shown in Fig. 5, and I preferably choose the supervisory relay OS as the relay to be associated with impedance coil I as in this manner I secure a more evenly balanced talking circuit as indicated in Fig. 7. That is at the answering end of the cord circuit a full winding is connected to the tip side and a half winding to the sleeve side while'at the calling end a half winding is connected to the tip sideand a full winding to the sleeve side of the cord circuit.

Now as to the ringing apparatus as H, when applying my invention to party line ringing I provide a well-known form of party line indicating key having contact sets 11, 12, 13, 1-1, corresponding in numberto the number of frequencies, these contacts being closed when the plungers are in their intermediate, locking or indicating position. A common contact 15 is also shown, this contact being adapted to be operated when any of the ringing plungers are in their fully actuated position and when the plunger-s restore to their indicating or locking positionthe contact 15 again closes as shown. In the preferred method of operation of Fig. 1, the proper ringing plunger is depressed before the calling plug P is inserted into a jack this arrangement being preferred because in using a locking party line ringing key one of the ringing contacts is always closed so that I prefer to select the frequency before the plugjis inserted into the called jack. In such case the contact 15 is not needed and is short circuited as shown at 16.

If it is desired to depend upon the operation of a ringing plunger after a plug has been inserted, then this connection 16 may be removed and in which case the operation of the contacts 15 interrupts the circuit through the low resistance non-inductive Winding 17 to permit the operation of relay OD. That is if it is desired that the ringing key should be operated after inserting the plug p, then connection 16 is opened and therefore relay OD does not operate upon inserting the plug 7) due to the low resistance shunt around OI) through the winding 17, but when this contact 15 is interrupted after plugging in, the relay ()1) energizes and although the shunt circuit is again closed when contacts 15 restore it does not cause a deenergization of OD. This is because of the well known fact that a relay will hold up on a small part of the current which is required to give it an initial energization.

As I preferably use the well-known harmonic ringing system I have provided four ringing generators 19, 20, 21, 22 which of course correspond to the call bells of the party line substation telephones. Each of the ringing generators is connected through a periodically closed contact, there being therefore four such contacts 23, 2 1, 25, 26, which may be operated by any source of power to periodically close the ringing contacts 27,28, 29, 30. In order to assure the operation of the relay RCR when the receiver is removed at the called substation, I provide a source of current 27 in connection with the ringing device II, which source is preferably a separate source from the talking battery, and may consist of dry cells, and has an opposite pole grounded so that when the vibrating contacts 23, to 26 are closed during the silent interval, this battery 27 is connected in series with the cord circuit battery giving a higher potential so that a more positive operation of relay ROE is secured. It will be apparent that the battery 27 be left out and theother terminal of the cord. circuit battery attached to these contacts 31 to 3A to secure the operation of ROB if desired. The test winding TEST is part of the operators induction coil, being used in a well known manner apparentfrom the drawing.

I have shown in connection with my invention, a so-called peg-count device K by which the number of answered calls of each operator is recorded. This device preferably comprises a relay 35 preferably of high resistance and impedance which is common to each operators position and which is adapted to be energized each time a plug 39 of its corresponding position is inserted to answer a call. The operation of the relay 35 closes a circuit through a counte1.'-1nagnet 36 and this records upon a meter, the answered call.

Having described in general the embodiment of my invention as illustrated in Fig. 1, its operation will now be described. Assuming a subscriber at substation C has removed his receiver to initiate a call, the line relay LR is energized over the calling line in a well known manner to operate the associated line signal whereupon the operator inserts an answering plug I into a jack J of the calling line. This operation establishes the energization of relays CO and AS. The operation of the cut-off relay CO is effected by a circuit traced from battery through the winding of impedance coil 1, the answering sleeve conductor, sleeve contacts of the plug and jack and the winding of CO to ground. Relay CO therefore energizes to disconnect the line relay LR and, in the present embodiment of my invention extend the conductors of line A to the answering end of the cord circuit. The receiver at the calling substation being off the hook, there is a flow of current through impedance coil I and out over the calling line returning over the tip side of the circuit and through the winding of the answering supervisory relay AS to ground. Relay AS therefore energizes and interrupts its normal contact 37 so that the lamp 3 can not be operated while the receiver is off the hook. Also responsive to the operation of relay AS, its alternate contacts 38, 39 are closed connecting the operators telephone 0 through the normally closed contacts 10, 4:1, to the answering end of the link circuit.

The operator now inquires the number of the wanted line and tests the jack of the called line with the tip of plug 79 in the usual manner and finding the line idle inserts the plug 29 into the jack j after having pressed the proper ringing plunger. This connects the sleeve oroperators disconnect relay OD in circuit with the cut-off relay 00 causing the energization of these relays by current over a circuit traced from battery through the winding of OD, sleeve contacts of p and j, the winding of co to ground. The operation of 00 removes the substation control of the line relay in the i usual manner and th e'operation of OD efing traced from generator 22 (which we -will assume is the connected generator by a reason of its operated contact 11) alternate contact 30, alternate contact 11, ringing conductor46, winding '4 and 5 in multiple, alternate contact 45, normal contact 8, tip side of the circuit over the calling line including the substationcall bell, returning over the sleeve side to point 47 where it divides, part of the current flowing through relay OD and battery to ground and part of the current flowing through normally closed contact 9, Winding 17, connection 16 and battery to a ground. Each periodic closure of alternate contact of the ringing device of course causes an operation of the call bell and when the subscriber removes his receiver in response to the call, and upon the following closure of alternate contact 34 of the ring- 'ing device H, due to the removal of the condenser at the substation a path for direct current through the Winding 4 of the ringing control relay ROR is established to causethe initial energization of this relay. As already stated, when the contact 34 is closed, the ringing battery 27, which by the way, may constitute dry cells as its circuit is only closed for short periods, is connected in series with the cord circuit battery, providing a higher potential for the operation of the ringing control relay than if only the cord circuit or talking battery only was used, this circuitbeing traced from battery 27, alternate contact 34 over the previously described path for ringing curr nt, back through relay OD and resistance 17 to the cord circuit battery. This flow of current through the initial energizing winding 4 of relay ROB causes the attraction of its armature whereby'its alternate contact 6 is first closed. The closing of this contact 6 connects the local energizing winding 7 in circuit and causes the continued attraction of the armature which interrupts normal contacts 8, 9, thereby disconnecting the ring ing current and closing alternate contacts 8, 9, to establish the continuity of the talking circuit. Theclosing of alternate, contact 8 connects the calling supervisory relay OS in circuit-with the line so that battery flowing through'the relay OD and out over the called line returns over the tip side and through alternate contact 8 and winding of OS to ground. Relay OS therefore operates'to interrupt its normal contact 44 and efiaces the signal 10. It will'also be noted that relay ROR interrupts its own initial energizing circuit through its normal contacts 8, 9, but not until the local circuit is closed. The substations O and D are now connected in a conversational circuit the battery supply being as indicated in the diagram 6. During the connection of the link circuit with the calling and called line it is impossible for the operator to listen in due to the fact that her telephone has been disassociated from the link circuit by reason of the interrupted contact 40, 41,which cannot be closed again until the plug 2) is withdrawn from the connected jack.

9 After the subscribers have finished conversation they will replace their respective receivers upon their switch-hooks, this act at the calling substation C causing the restoration of answering supervisory relay AS and the lighting of the answering supewisory signal 3, while the restoration of the receiver at the called substation D causes the restoration of calling supervisory relay OS and the lighting of the calling supervisory signal 10. The operator in response to this signal knows that disconnection is desired and removes the plugs 29 and P from their respective jacks, the withdrawal of plug 79 causing the restoration of OD and by reason of the interruption of its alternate contact 42 the consequent restoration of relay ROR. The apparatus of cord circuit G is now at normal and the link circuit available for use in establishing other connections.

If it is desired to operate the ringing key after the plug 79 is inserted, then the connection 16 is disconnected so that the connection from battery through resistance 17, extends through the normally closed common contact 15 of the ringing key. Furthermore the resistance 17 is made sufliciently low to prevent the energization of OD in multiple with resistance 17 when the plug 7) is inserted in the jack and OD and 17 are connected with cut-ofi' relay 00. Therefore, with such arrangement when the operator inserts the plug 79 into the jack of a called line, the relay OD does not operate although the cut-ofi relay of the called line does. Upon operating the ringing key, common contact 15 is interrupted thereby interrupting the shunt circuit through resistance 17 whereby suflicient current will flow through OD to cause its operation. Now when the operator allows the ringin key to restore to its locking position and the contact 15 is again closed, although the shunt circuit through resistance 17 is again closed, relay OD does not restore due to the well-known fact that a relay once energized can be maintained energized on acornparatively small amount of its initial energizing current. Therefore, when the relay OD operates, the subsequent application of ringing current and control of the supervisory lamps is the same as that previously described in connection with Fig. 1 with conductor 16 connected as'shown.

Fig. 2.

In Fig. 2 I have illustrated my invention embodied in a so-called three wire system,

that is a system in which three conductors are providedfor the multiple jacks, and the cut-ofi relay is connectedto a contact of the jack independent of the talking circuit; and likewise three contacts are providedfor the connecting plugs, two of the contacts of the answering and calling plugs being connected together by the talking conductors while the third contact of each of the plugs is connected to a terminal of the battery so as to effect an energizing circuit for the cut off relay independent of the talking circuit. In the apparatus of Fig. 2, on parts which correspond to parts of Fig. 1, I have used reference characters similar to that of Fig. 1, but with the exponent prime so that the system of Fig. 2will be easily understood after an understanding of the system of Fig. 1.

In the embodiment of my invention as illustrated in Fig. '2, due to the fact that the cut-off relay is energized over a circuit independent of the'talking strands, I preferably use double wound supervisory relays as AS and CS bridging them across'the talking conductors of their respective ends. Therefore, in this particular embodiment, no construction as of Fig. 5, is necessary. Also in Fig. 2 the operators disconnect relay OD is connected to the third conductor of the calling plug so that when the plugis inserted into the jack, the cut-off and disconnect relays are connected in series and energized.

The protective resistance 50 which is connected between battery and the third contact of the answering plug may be a non inductive resistance and wound upon the core of one of the cord relays in order to follow out the four unit relay principle. This is also true of resistances 17 and 17 0 Also in Fig. 2, the connection from key contact 15? differs slightly in that a separate shunt resistance is provided but the control of relay OD by the ringing key is the same.

It will be noted that the connection at 16 is open, so that the ringing key must be depressed before plugging in, but to arrange Fig. 2 so as tooperate the ringing key after plugging in the connection 16 is closed.

Operation of Fig. 2.

' Assuming now that a subscriber at the sub'stationof line A desires to communicate w th a substatlon on line 13 preferably substation as D which is like D of Fig. 1 but not shown, the receiver is removed at the calling substation to energize the associated linerelay L11 and light the line signal. The operator in response to this signal inserts the answering plug P into the jack J of the callingline, whereby the cut-off relay CO reslstance 50 and battery are connected 1n c1rcu1t causing the energlzation of the cut-off relay and consequently the restoration of the line relay and lamp signal.

Also upon inserting plug P in the jack, the answering supervisory relay AS and the, cord circuit battery are connected in bridge of the calling line, and therefore relay AS? energizes-to close its contacts 38 39 and due to the fact that the disconnect "relay OD is still at normal, and its'normal contacts 40 11 are still closed, the operatoris telephone 0 is connected in bridge of the answering end of the cord circuit so that the operator may ascertain thewants of the calling subscriber. Finding that the substation D is the wanted substation, after testing in the usual manner and finding B idle, the operator inserts the calling plug 72 into a jack j of the wanted line, thereby connecting the disconnect relay OD and the cut-ofi relay 00 in series over the third conductor, causing their energization. Upon energization of CD its normal contacts 40 41 are interrupted to disconnect the operators telephone 0 Having previously depressed the proper ringing plunger, which we will assume is the one that closedcontacts 11 calling generator 22 is connected to the called line to ring the bell of substation D in a manner as described in connection with Fig. 1.

Upon response of the called subscriber,

the ringing relay RCIt is operated in a manner as described in connection with Fig. 1 whereby the ringing current is disconnected and the calling supervisory relay CS and cord circuit battery are connected in supervisory signals 3 ,10 .inresponse to this disconnect signal withinterrupting theenergizing circuit of the supervisory relays 'AS and CS causing their restoration and the relighting of The operator draws the connecting plugs, thus restoring all of the apparatus to normal.

ihodlment of lnventlon, dlfl'ermg 1n some InFig. 3, I have illustrated another em- -respectsfrom the systems of Figs. 1 and 2.

- In the present embodiment of my invention 'when the operator responds to a call, her telephone set O is automatically connected connect her telephone to the cord circuit while it is connecting two telephone lines, but she may only do this if either one one,- bothof the substations are out of conversationalassocia-tion. That is to say, with two .7

lines connected by acord circuit G as long as the two receivers are off the switch hooks,

,and the substations are connected in a conversational circuit, the operator is unable to connect her telephone to the cord circuit, but should either one or both of the receivers be on their switch-hooks, then she is able to connect her telephone to the con- .neeted cord circuit.

To this end I have added a manualkey R to each cord circuit, and a common operators relay OR to each position, the relay OR being connected as unable to listen 1n during a conversational .indicated.

A reason for the above hstenmg-ln arrangement is that although the operator is connection between two substations, should one of the subscribers hang up for'disconnection and the other subscriber signal the operator for further communication, the

1 operator may again associate her telephone O Wlth the connected cord circuit Without withdrawing the calling plug 79 from the jacket the called line as would be necessary in the systems of Figs. 1 and 2.

Each cord circuit G is provided Wlfll a "manually operated key R, and for each op- 'erators position of a plurality ofcord cir cuits. a common operators relay OR is provided. which is multiply connected to each of 'thekey contacts 53 and corresponding I alternate contacts 54, 37 of the supervisory relays CS AS -Ito ground at alternate con tact 42 ofrelay OD Thus with the connecting plugs inserted in the line jacks, as

long as the receivers are off the switch hooks ofa connected pair of lines. the relays AS and CS? are'energized so that if an associated operatorskey R is operated, a circuit for the common relay 0B web lished causing its energization and therefore the interruption of its alternate. contacts 55, 56, to disconnect the operators telephone O If either of the relays A8 CS is back, the closing of contacts 53 of an operators key does not operate relay OR to disconnect the operators circuit. While I have shown a specific arrangement for controlling relay OR through the listening-in key and the line controlled relays A3 CS many other circuit arrangements will readily suggest themselves, and therefore I do'not wish to be limited to the particular arrangement shown.

The operation of'the supervisory apparatus and-ringing apparatus of cord circuit G2 otherwise is the same as that of Fig. a, the like parts being indicated by like reference characters, except that in Fig. 3 the ref-- erence characters have the suiiix 2. \Vith this explanation it is thought that the operation of Fig. 3 will be apparent without again going into the detailed operation thereof.

Fig. 4.

In Fig. 4 I have illustrated another embodiment of my invention, the automatic ringing control of this system being the same as that of Fig. 3, but the control of the operators telephone 0 differs slightly from that of Fig. 3 in that the operators the cord circuit if either one or both of the substations are out of conversational assoclatlon wlth the cord circuit. In the present figure'the common operators relay OR is connected through alternate contacts 549. 58 of the calling and answering supervisory relays and then through alternate contacts 53 of the key R this circuit being in series through said contacts so that if thekey R 1s thrownwith both of the supervisory relays AS and CS energized, a circuit for the operators relay 0B is established causing its energfization and preventing connecting the telephone set to the cord circuit. But if either relay A8 or CS is back, the closing of contacts 53 of key B does not energize 0B and therefore the operation of R connects the telephone 0 in circuit with the cord.

In the operation of the system of Fig. 4 when the operator answers a call by inserti g the answering plug P into a ca ing jack, she will throw the key R thereby con,- necting the telephone 0 through the contacts of key R to the answering end of the cord circuit. At this time it will be understood although relay A8 is energized, relay CS has not energized as yet, so that no circuit can be closed for the operators relay 0B and therefore an answering connection is established. After the calling plug 72 is inserted into the jack of a called line, and before the relay CS energizes, the operator may at any time by throwing the key R connect her telephone in circuit with the cord circuit G but after the called subscriber has responded and the calling supervisory relay CS has energized so that the two lines are in a conversational connection, the operation of the key R will close contacts 53 and therefore an energizing circuit for relay 0B is established because contacts 54-, 58 are closed, causing it to interrupt its normal contacts 55 56 so that the operation of key R is ineffective, Of course, as long as one or both of the receivers are upon their switch-hooks and one or both of the supervisory relays deenergized, the operation of key R is effective because no energizing circuit for the common relay 0B is established.

From the above it will be seen that in the system of Fig. 4:, the operator must always throw her key R whether it be an answering, or subsequent listening-in operation, to connect her telephone to a cord circuit as distinguished from Fig. 3 in which the oper ators key It need be thrown only upon a subsequent listening-in connection.

In Fig. 4, I have connected the ringing key common contact 15 through a normally closed contact 60 on CD so that when using the system with a subsequent ringing key operation, the ensuingoperation of OD interrupts contacts 60 thereby removing the shunt circuit of CD which includes resistance 170 and effecting a more positive holding circuit for OD What I claim as new and desire to se cure by United States Letters Patent is:

1. A metallic circuit telephone system comprising telephone lines, a two conductor link circuit having answering and calling terminals for interconnecting said lines, ringing apparatus and a pair of supervisory signals for the link circuit, an an swering supervisory relay for said link circuit, means for placing said relay under the control of a calling line upon the connection to said line by the answering end of the link circuit for controlling one of said signals, a second relay having an energizing circuit including a calling terminal of the link circuit and a connected called line for connecting said ringing apparatus to a called line, a third relay having contacts operated upon response from a called Substation for' disconnecting said ringing apparatus, a locklng circuit for sa1d last relay for preventing its reoperation, and a fourth relay controllable over the two conductors of the called line in series for controlling relay for said link circuit, means for placing said relay under the control of a calling line upon connection to said line by the answering end of the link circuit for controlling one of said signals, a second relay responsive to the connection of the calling end of the link circuit to a called line for connecting said ringing apparatus to the called line, a third relay having contacts operated upon a response from a called substation for disconnecting said ringing apparatus and for connecting the ends of said link circuits, and a fourth relay controllable over the called line for controlling the other supervisory signal.

3. A telephone system comprising tele phone lines, a secret service and automatic ringing link circuit for interconnecting said lines, an operators telephone and ringing apparatus for the link circuit, said link circuit comprising four relays, a relay operated upon connection of said link circuit with the calling line for automatically connecting the operators telephone to the link circuit, a second relay operated upon connection with the called line by the link circuit for automatically disconnecting the telephone and connecting said ringing apparatus to the called line, a third relay operated upon response from the called substation to automatically disconnect said ringing apparatus, and a fourth relay normally disconnected from the calling end of the link circuit but controllable over the called line for controlling a supervisory signal.

4. A telephone system comprising telephone lines, a link circuit for connecting to said lines, a control relay, means for connecting said relay in circuit with one of said lines upon connection made therewith, an 1n1t1al energizing circuit for sa1d relay ncluding normally closed contacts thereof,

said telephone line and a source of current,

a maintaining circuit for said relay having a normally open contact controlled by said relay whereby when said relay is initially energized said normally open contact is closed to render said maintaining circuit effective to cause a continued operation of the control relay to interrupt the normally closed contacts.

5. A telephone system comprising telephone lines, a link circuit for connecting to said lines,; a control relay, means for con- "necting said relay in circuit with one of :sa-id lines upon connection made with said line by the link circuit, an initialenergizing circuit for said relay including said telephone hue and a source ofcurrent,ama1ntaining circuit for said relay also including said source and having a normally open contact controlled by said relay wherebywhen said relay is initially energized said normally open contact is closed to render said maintaining clrcult effectiveto cause a continued-operation of the control relay, and other contacts for said relay operated only by such continued operation of the control relay. p 6. A telephone system comprising telephone lines'of various resistances. alink circuit for connecting to said lines, a relay for said link circuit, an initial energizing circuit for said relay including a connected one of said telephonelines and a source of current, a plurality of contacts for said relay, means for operating only one of said contacts upon the initial energization oi said relay, a maintaining circuit for said relay also including said source and closed responsive to said contact whereby a continued operationof said relay is effective to cause the operation of the other contacts therefor.

- 7. A telephone system comprising telephone lines, an operators link circuit for interconnecting said lines, an answering supervisory relay and an operators disconnect relay for the link circuit, a supervisory lamp operated by each relay, an operators telephone, means responsive to the connection of the answering end of the link circuit to a calling line for operating said answering supervisory relay for connecting the operators telephone to the link circuit,

. means whereby the connection of the calling nected to said relays, circuit connections whereby Whenthe answering end of the link circuit is connected to a calling line said current will flow through the associated relay to effect its energization and supply talking current to the calling telephone, contacts controlled by saidrelay when so energized for connecting the operators telephone to the link circuit, circuit connections whereby when the calling end of the link circuit is connected to a called line said current .will flow through the associated relay to eifect its energization and supply talking current to the called telephone, and con tacts interrupted by said last relay when so energized for disconnecting the operators telephone from the link circuit, and supervisory lamps lighted and elfaced by said relays.

9. A telephone system comprising telephone lines, an operators link circuit ioi interconnecting said lines, an operators telephone, an answering supervisory relay and asignal controlled thereby, an operators disconnect relay, a calling supervisory relay controlled over circuit connections including normally interrupted contacts on the disconnect relay, a source of current for energizing the answering siupervisory relay responsive to connection of the answering end of the link circuit to a calling line, contacts closed by said supervisory relay when so energized for connecting the operatoNs telephone to the link circuit, and circuit connections whereby the connection of the call-- ing end of the link circuit to a called line will effect the operation of the disconnect relay for disconnecting the operators tele phone from the link circuit.

10. A telephone system comprising tele phone lines, an operators link circuit for interconnecting said lines, an operators telephone, an answering supervisory relay energized responsive to the connection of the answering end of the link circuit to a calling line for connecting said operators telephone to the link circuit, an operators disconnect relay energized responsive to connection of the calling end of the link circuit to a called line for disconnecting the operators telephone from the link circuit, supervisory apparatus operatively asso ciated with the calling end of the link circuit responsive to such energization of the disconnect relay, and a response supervisory relay normally disconnected from the call.- ing end of the link circuit for assisting in the control of said supervisory apparatus.

11. A telephone system comprising telephone lines, cut-oii' relays for said lines, an operators link circuit for interconnecting said lines, a relay at each end of the link circuit, circuit connections whereby each link relay and a cut-oil relay are energized when connection is made between the link circuit and calling and called lines, an operators telephone connected to and discounected from said link circuit by the operation of said link relays, and a source of talking current adapted to be connected to said lines through the windings of said relays.

12. A telephone system comprising telephone lines, an operators link circuit for interconnecting said lines, an operators telephone, an answering end supervisory relay for connecting said telephone to the link responsive to Connection of said link and a calling line, a calling supervisory lamp, a relay energized responsive to connection of the calling end of the link to a called line for disconnecting the operators telephone and lighting said lamp, and a source of talking current adapted to be connected to said lines through the windings of said relays.

13. A telephone system comprising telephone lines, an operators link circuit for interconnecting said lines, supervisory signals for the link circuit, an operators telephone, a pair of supervisory control relays for the link circuit for automatically connecting the operators telephone to and disconnecting it from the link circuit, and a source of talking current adapted to be connected to said lines through the windings of said relays.

14. A telephone system comprising an operators cord circuit having answering and calling plug terminals, answering and calling supervisory signals, normally inoperative circuits for said answering and calling signals controlled by said answering and calling relays respectively, a third relay having an energizing circuit connected to the calling terminal, and a circuit for rendering said signals operative including normally open contacts of said third relay.

15. A telephone system comprising telephone lines, an operators link circuit for interconnecting said lines, an operators telephone, an answering response supervisory relay for connecting said telephone to the link circuit when said link circuit is connected to a calling line, a calling sleeve supervisory relay for disconnecting said operators telephone from said link circuit responsive to the connection of said link circuit to a called line.

16. A telephone system comprising telephone lines, an operators link circuit for interconnecting said lines, an operators telephone, an answering response supervisory relay for connecting said telephone to said link circuit when said link circuit is connected to a calling one of said lines, a calling supervisory relay responsive to the connection of said link circuit to a called one of said lines for disconnecting the operators telephone from said link circuit, and supervisory signals for said link circuit controllable by said relays.

17. A telephone system including a calling subscribers line and a called subscribers line, an operators link circuit provided with an answering terminal and a calling terminal, a response supervisory relay associated with said answering terminal for connecting an operators telephone to said, link circuit, a supervisory relay associated. with said calling terminal responsive to connection of the calling end of the link to said called line for disconnecting the operators telephone.

18. A telephone system comprising telephone lines, cut-off relays for said lines, an operators link circuit provided with a pair of talking conductors for interconnecting said lines, a relay at each end of said link circuit, circuit connections whereby each link relay and one of said cut-off relays are energized when connection is made between the link circuit and calling and called ones of said lines, and an operators telephone adapted to be bridged across and disconnected from the conductors of said link circuit by the operation of said link relays.

19. A telephone system comprising telephone lines, a two-conductor operators link circuit for interconnecting said lines, an operators telephone, an answering end relay for bridging said telephone across the conductors of said link circuit, a calling end relay energized responsive to connection of the calling end of said link circuit to a called line for disconnecting the operators telephone from across the conductors of said link circuit, an answering supervisory signal and a calling supervisory signal, and circuits for said signals controllable by said calling end relay.

20. A telephone system comprising telephone lines, an operators link circuit provided with a pair of talking conductors for interconnecting said lines, an answering and a calling supervisory signal for said link circuit, an operators telephone, a pair of supervisory control relays for the link circuit for automatically bridging the operators telephone across the conductors of said link circuit and for disconnecting it from the conductors of said link circuit, and circuits for said supervisory signals controllable by said supervisory control relays.

Signed by me at Chicago, county of Cook and State of Illinois, in the presence of two witnesses.

HIRAM D. CURRIER.

Witnesses:

G. E. MUELLER, B. OBRIEN.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. G. 

